1. Field of the Invention
The present invention relates to a substrate processing method and apparatus for forming an amorphous silicon film on a monocrystalline substrate having an insulating film formed on at least a surface portion thereof and an exposed silicon surface.
2. Description of the Prior Art
There are conventional substrate processing methods and apparatuses for forming an amorphous silicon film on a monocrystalline substrate having an insulating film formed on at least a surface portion thereof and an exposed silicon surface.
However, such conventional substrate processing methods and apparatuses have limitations, such as a low film forming rate when a silicon film is formed at a low temperature and non-uniformity in film thickness when a silicon film is formed using highly reactive gas.
That is, in the related art, if a substrate is processed by, for example, a lateral solid phase epitaxial growth method, fine crystalline grains are easily formed between amorphous silicon (a-Si) and an insulating film, and in this case, when heat treatment is performed for monocrystallization of Si, the fine crystalline grains grow and make the monocrystallization of Si difficult.
To suppress growth of such fine crystalline grains, a-Si can be grown at a low temperature. For example, in the case of a chemical vapor deposition (CVD) method using SiH4, a-Si may be reliably grown at a temperature of 580° C. or lower because 600° C. is a boundary temperature between a-Si growth and polysilicon (poly-Si) growth. Therefore, in the CVD method using SiH4, the film forming temperature may be kept equal to or lower than 580° C.
However, in the case of such a low-temperature process, the film forming rate is low. For example, if the film forming process is performed at 80 Pa and 580° C., a-Si grows at a rate of about 6 nm/min; however, if the process temperature reduces to 530° C., the growing rate of a-Si reduces to about 2 nm/min.
To increase the growing rate reduced due to a low process temperature, highly reactive gas such as Si2H6 can be used. If Si2H6 is used as process gas, the growing rate can be maintained at about 3 nm/min even when the pressure and temperature of a film forming process are low at about 25 Pa and 500° C.
However, in the case where highly reactive gas is used as process gas, the thickness uniformity of a film is deteriorated. For example, if a film is formed on a φ200-mm substrate (wafer) at 530° C. by using SiH4 as process gas, the in-plane thickness uniformity of the film can be within ±1%. However, if a film is formed on a φ200-mm substrate at 500° C. by using highly reactive Si2H6 as process gas, the in-plane thickness uniformity of the film is deteriorated to a level greater than ±5%.
As explained above, according to the conventional substrate processing methods and apparatuses, a substrate cannot be processed with good in-plane film thickness uniformity while maintaining the film forming rate at a desired level.